1. Field of the Invention
The present invention relates to a hydraulic circuit for supplying pressure oil to a plurality of actuators, etc., and more particularly to a hydraulic circuit for use in construction machines such as a crawler vehicle provided with a plurality of actuators, including a hydraulic excavator.
2. Description of the Related Art
Known hydraulic circuits for use in construction machines such as a crawler vehicle are disclosed in, e.g., Japanese Unexamined Patent Application Publication Nos. 4-118428 and 57-184136. Those disclosed hydraulic circuits are used in construction machines provided with a pair of right and left hydraulic travel actuators (crawler travel devices) and hydraulic work actuators (such as a bucket, a boom, an arm, and a swivel), and include directional control (selecting) valves for controlling a direction of connection between a hydraulic pump or tank and each actuator and a flow rate of pressure oil therebetween in order to operate the actuator.
In each of the hydraulic circuits disclosed in Japanese Unexamined Patent Application Publication Nos. 4-118428 and 57-184136, pressure oil is supplied from three first to third hydraulic pumps, and each of these hydraulic pumps is connected to three hydraulic circuits including respectively directional control valves for the right and left hydraulic travel actuators (hereinafter referred to as xe2x80x9cright and left travel directional control valvesxe2x80x9d) and a directional control valve for the swivel actuator (hereinafter referred to as a xe2x80x9cswivel directional control valvexe2x80x9d). More specifically, the first and second hydraulic pumps are connected to hydraulic circuits (hereinafter referred to as xe2x80x9cfirst and second circuitsxe2x80x9d) each including the right or left travel directional control valve and the directional control valves for the other work actuators (hereinafter referred to as xe2x80x9cother work directional control valvesxe2x80x9d), while the third hydraulic pump is connected to a hydraulic circuit (hereinafter referred to as a xe2x80x9cthird circuitxe2x80x9d) including the swivel directional control valve, etc. Such an arrangement ensures independency of the swivel operation from the operation of the other actuators.
Then, any of those hydraulic circuits includes a selector valve (combined operation control valve, hereinafter referred to as a xe2x80x9cmerging valvexe2x80x9d) for changing over the third pump, which is connected to the third circuit, to be connectable with the first or second circuit as well. Upon shift of the merging valve, the pressure oil from the third pump can also be supplied to the first or second circuit so that when the travel actuator and the other work actuator(s) both connected to the first or second circuit are operated at the same time, the pressure oil is supplied at a sufficient flow rate to the other work actuator(s).
In the hydraulic circuit disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 4-118428, the merging valve is connected to a hydraulic line led out of the side upstream of the swivel directional control valve (swivel control valve), thus enabling the pressure oil to be supplied to the first or second circuit through the associated hydraulic lines. With such an arrangement, the pressure oil from the third pump can be supplied to the other work actuators in the first or second circuit upon the shift of the merging valve. In the merging mode, however, there is a fear that the pressure oil is supplied at a larger flow rate to one of the other work actuators in the first and second circuits, which is subjected to a lower load, and the pressure oil supplied to the swivel directional control valve, etc. in the third circuit (including a directional control valve connected to a blade cylinder in the above-cited Japanese Unexamined Patent Application Publication No. 4-118428) is reduced. This may deteriorate the operability of the actuators connected to those directional control valves.
Also, in the hydraulic circuit disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 57-184136, the merging valve is connected to the third circuit downstream of the swivel directional control valve, thus enabling the pressure oil to be supplied to the other work actuators in the first or second circuit (first directional control valve group in the above-cited Japanese Unexamined Patent Application Publication No. 57-184136). With such an arrangement, when the swivel directional control valve in the third circuit is shifted to such an extent that an unloading line is closed, the pressure oil is no longer supplied to the merging valve. In such a case, therefore, the pressure oil from the third pump cannot be supplied to the other work actuators in the first or second circuit.
In view of the state of the art mentioned above, it is an object of the present invention to provide a hydraulic circuit, which can efficiently distribute pressure oil supplied from a third pump connected to a third circuit to a first and/or second circuit as well, and can improve the operability of actuators.
To achieve the above object, the present invention provides a hydraulic circuit for driving actuators by pressure oil supplied from a first pump, a second pump and a third pump and returned to a tank, the hydraulic circuit comprising a first circuit including a directional control valve supplied with the pressure oil from the first pump, the directional control valve in the first circuit controlling connection between the first pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a second circuit including a directional control valve supplied with the pressure oil from the second pump, the directional control valve in the second circuit controlling connection between the second pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a third circuit including a directional control valve supplied with the pressure oil from the third pump, the directional control valve in the third circuit controlling connection between the third pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a first merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the first circuit; a second merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the second circuit; and a merging valve for selectively communicating or cutting off the first merging line and the second merging line with or from the third pump, the merging valve having a first shift position at which the third pump is connected to the second merging line, and a second shift position at which the third pump is connected to the first merging line and the second merging line, the merging valve being continuously shifted between the first shift position and the second shift position depending on a state of the first circuit or the second circuit.
In the hydraulic circuit constructed as set forth above, preferably, when the directional control valve in the first circuit is not operated, the merging valve is shifted to the first shift position, and when the directional control valve in the first circuit is operated, the merging valve is shifted toward the second shift position depending on a state of operation of the directional control valve in the first circuit.
Alternatively, in the hydraulic circuit constructed as set forth above, the merging valve may be continuously shifted between the first shift position and the second shift position depending on a flow rate of the pressure oil required by the directional control valve in the first circuit or the second circuit so that the pressure oil from the third pump is distributed and sent to the first circuit or the second circuit under a pressurized state.
With the above features, when the directional control valve in the first circuit is not operated, the merging valve is shifted to the first shift position, whereupon a part of the pressure oil sent to the third circuit under the pressurized state can be supplied to the second circuit, which requires supply of the pressure oil, without wasteful loss while preventing that part of the pressure oil from being supplied to the first circuit in which the directional control valve is not operated. Also, when the directional control valve in the first circuit is operated, the merging valve is shifted to the second shift position so that surplus pressure oil sent from the third pump under the pressurized state can be supplied to not only the second circuit but also the first circuit. Further, when the flow rate of the pressure oil supplied to the actuator with the operation of the directional control valve in the first circuit (i.e., the flow rate of the pressure oil required by that directional control valve) is small, the pressure oil is sent from the third pump to the second circuit at a larger flow rate. As the flow rate of the pressure oil required by the directional control valve in the first circuit increases, the merging valve is shifted toward the second shift position proportionally, thereby increasing the flow rate of the pressure oil supplied from the third pump to the first circuit and decreasing the flow rate of the pressure oil supplied from the third pump to the second circuit. Thus, the pressure oil supplied from the third pump connected to the third circuit can be efficiently distributed to the first and/or second circuit.
The present invention also provides a hydraulic circuit for driving actuators by pressure oil supplied from one pump and the other pump and returned to a tank, the hydraulic circuit comprising one circuit including a directional control valve supplied with the pressure oil from the one pump, the directional control valve in the one circuit controlling connection between the one pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; the other circuit including a directional control valve supplied with the pressure oil from the other pump, the directional control valve in the other circuit controlling connection between the other pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a merging line disposed to be capable of supplying the pressure oil sent from the other pump under a pressurized state to the directional control valve in the one circuit; and a merging valve for selectively communicating or cutting off the merging line with or from the other pump, the merging valve being capable of sending the pressure oil from the other pump under a pressurized state to the one circuit and reducing an opening degree of a throttle disposed between the other pump and the tank depending on a flow rate of the pressure oil required by the directional control valve in the one circuit, thereby increasing a flow rate of the pressure oil sent to the one circuit under the pressurized state.
In the hydraulic circuit constructed as set forth above, the one circuit may comprise two first and second hydraulic circuits each including a directional control valve.
With the above features, since the pressure oil not required by the directional control valve in the one circuit is returned to the tank, the pressure oil from the other pump can be efficiently supplied to the one circuit under the pressurized state without imposing overload on the other pump.
Further, the present invention provides a hydraulic circuit for driving actuators by pressure oil supplied from one pump and the other pump and returned to a tank, the hydraulic circuit comprising one circuit including a directional control valve supplied with the pressure oil from the one pump, the directional control valve in the one circuit controlling connection between the one pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; the other circuit including a directional control valve supplied with the pressure oil from the other pump, the directional control valve in the other circuit controlling connection between the other pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a merging line disposed to be capable of supplying the pressure oil sent from the other pump under a pressurized state to the directional control valve in the one circuit; and a merging valve for selectively communicating or cutting off the merging line with or from the other pump, the merging valve having a shift position at which the side upstream of the directional control valve in the other circuit is connected to the one circuit through a throttle and the side downstream of the directional control valve in the other circuit is also connected to the one circuit.
In the hydraulic circuit constructed as set forth above, the one circuit may comprise two first and second hydraulic circuits each including a directional control valve.
With the above features, the pressure oil sent from the other pump under the pressurized state can be supplied to the one circuit while supplying the pressure oil from the other pump to the other circuit. In addition, surplus pressure oil drained from the side downstream of the directional control valve in the other circuit can also be supplied to the one circuit under the pressurized state. Accordingly, the pressure oil from the other pump connected to the other circuit can be efficiently distributed to the one circuit, and the operability of the actuator connected to the one circuit can be improved.
Still further, the present invention provides a hydraulic circuit for driving actuators by pressure oil supplied from a first pump, a second pump and a third pump and returned to a tank, the hydraulic circuit comprising a first circuit including a directional control valve supplied with the pressure oil from the first pump, the directional control valve in the first circuit controlling connection between the first pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a second circuit including a directional control valve supplied with the pressure oil from the second pump, the directional control valve in the second circuit controlling connection between the second pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a third circuit including a directional control valve supplied with the pressure oil from the third pump, the directional control valve in the third circuit controlling connection between the third pump or the tank and at least one of the actuators and a flow rate of the pressure oil therebetween; a first merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the first circuit; a second merging line disposed to be capable of supplying the pressure oil sent from the third pump under a pressurized state to the directional control valve in the second circuit; and a merging valve for selectively communicating or cutting off the first merging line and the second merging line with or from the third pump, the merging valve having a shift position at which the third pump is connected to the first merging line and the second merging line, the shift position establishing a state that the side upstream of the directional control valve in the third circuit is connected to the first circuit through a first throttle, the side upstream of the directional control valve in the third circuit is connected to the second circuit through a second throttle, and the side downstream of the directional control valve in the third circuit is connected to the first circuit.
With the above features, the pressure oil sent from the third pump under the pressurized state can be supplied to the first and second circuits while supplying the pressure oil from the third pump to the third circuit. In addition, surplus pressure oil drained from the side downstream of the directional control valve in the third circuit can also be supplied to the first circuit under the pressurized state. Accordingly, the pressure oil from the third pump connected to the third circuit can be efficiently distributed to the first circuit and the second circuit, and the operability of the actuators connected to the first and second circuits can be improved without reducing the operability of the actuator connected to the third circuit.
The hydraulic circuit constructed as set forth above may further comprise sub-valves operating in interlock with the directional control valves in the first circuit and the second circuit, the sub-valves generating a pilot pressure for shifting the merging valve to the aforesaid shift position. Also, the hydraulic circuit may further comprise detecting means disposed in a line for the pilot pressure, the detecting means detecting a state of operation of the corresponding actuator.
With the above features, the state of operation of the actuators can be detected by utilizing the sub-valves and the pilot hydraulic system for shifting the merging valve. Accordingly, it is possible to obviate the need of adding a special circuit only dedicated for detecting the state of operation of the actuators, and to prevent an increase in size of devices such as the directional control valves.
Still further, the present invention provides a hydraulic circuit for use in a traveling construction machine including actuators driven by pressure oil supplied from a hydraulic pump under a pressurized state and returned to a tank, and provided with a safety device for informing surroundings of the fact the construction machine is traveling, the hydraulic circuit comprising a travel control valve for controlling connection between the hydraulic pump or the tank and a travel actuator of the actuators and a flow rate of the pressure oil therebetween; and a travel signal hydraulic line for generating a travel signal upon operation of the travel control valve, the safety device being operated in accordance with a state of the travel signal hydraulic line.
Still further, the present invention provides a hydraulic circuit for use in a construction machine having an auto-idle function of controlling a rotational speed of a driving source for a hydraulic pump depending on a state of operation of each of actuators driven by pressure oil supplied from the hydraulic pump under a pressurized state and returned to a tank, the hydraulic circuit comprising a travel control valve for controlling connection between the hydraulic pump or the tank and a travel actuator of the actuators and a flow rate of the pressure oil therebetween; another control valve for controlling connection between the hydraulic pump or the tank and other one of the actuators than the travel actuator and a flow rate of the pressure oil therebetween; a travel signal hydraulic line for generating a travel signal upon operation of the travel control valve; and an auto-idle signal hydraulic line for generating an auto-idle signal upon operation of the other control valve, the rotational speed of the driving source being controlled in accordance with a state of the travel signal hydraulic line and a state of the auto-idle signal hydraulic line.
With the above features, since the hydraulic line for detecting the state of operation is divided into one for the travel directional control valve and the other directional control valve, the hydraulic circuit can include in more efficient arrangement not only a system for detecting the operations of both the travel directional control valve and the other directional control valve as required for detecting the auto-idle signal, but also a system for detecting the operation of only the travel directional control valve as required for operating a safety device. It is hence possible to obviate the need of adding a special circuit only dedicated for detecting the state of the travel operation, and to prevent an increase in size of devices such as the directional control valves.